Conventionally, there have been air conditioning controlling systems that control flow rates of hot and cold water to an air conditioner (referencing, for example,] Japanese Unexamined Patent Application Publication H11-211191 and Japanese Unexamined Patent Application Publication H06-272935). In these air conditioning controlling systems, flow rate controlling valve are provided in the supply routes for hot water/cold water to the air conditioner, where the valve unit within the flow rate controlling valve is driven to adjust the amount of opening of the flow path through which the hot/cold water flows.
Normally, in a flow rate controlling valve, an opening setting (a valve opening setpoint) is inputted from the air conditioning controlling device, and with the actual opening of the valve unit, detected by a valve opening detector, as a valve opening a measured value, the valve unit is driven so as to cause the valve opening measured value to match the valve opening setpoint. As a result, a fluid will flow in the flow path in which the flow rate controlling valve is equipped, flowing with a desired flow rate that has been provided as the valve opening setpoint. Such a flow rate controlling valve is known as an “opening control-type flow rate controlling valve.”
On the other hand, in recent years there have been flow rate controlling valves wherein a function for measuring the actual flow rate of the fluid that flows within the flow path has been added to the flow rate controlling valve itself, where a flow rate setting (a flow rate setpoint) corresponding to the conventional opening setting (the valve opening setpoint) has been sent from the air conditioning controlling device, and the driving of the valve unit is controlled within the flow rate controlling valve so as to cause the flow rate setting (the flow rate setpoint) that has been received and the actual flow rate (the measured value for the flow rate) to match. As a result, the fluid within the flow path wherein the flow rate controlling valve is installed will flow at the desired flow rate, which has been provided as the flow rate setpoint. Such a flow rate controlling valve is known as a “flow rate control-type flow rate controlling valve.”
For example, Japanese Unexamined Patent Application Publication 2009-245096 discloses a flow rate controlling valve comprising a motor that rotates a valve rod that is connected to a valve unit, a valve opening detector for detecting the actual opening of the valve unit, from the rotational position of the valve rod, and an actual flow rate measuring portion (actual flow rate calculating portion) for calculating the actual flow rate based on the differential pressure across the valve unit. In the flow rate controlling valve disclosed in Japanese Unexamined Patent Application Publication 2009-245096, when in an opening controlling mode, the amount of rotation of the valve rod by the motor is controlled so as to cause the valve opening measured value to match the valve opening setpoint, where the valve opening measured value is the actual opening of the valve unit detected by the valve opening detector, and when in a flow rate controlling mode, the amount of rotation of the valve rod by the motor is controlled so as to cause the measured value for the flow rate to match the flow rate setpoint, where the measured value of the flow rate is the actual flow rate calculated by the actual flow rate measuring portion (the actual flow rate calculating portion).
However, typically, in a flow rate controlling valve of a type wherein a valve rod, which is connected to the valve unit, is driven by a motor, the load torque will vary depending on the degree of opening. The load torque will be at a maximum in a nearly fully-closed state, wherein the differential pressure is at a maximum, based on a constant flow rate for the inflow from the primary side of the flow path of the valve, and the differential pressure will decrease as the valve begins to open from there, with the load torque decreasing commensurately.
On the other hand, because electric actuators for driving valves are designed with output torques (the torque generated by the motor, the gear reduction ratio, and the like) matching the maximum load torque on the valve side (that is, the load torque when the valve is nearly fully close), if the design is with, for example, a low-power motor and a gear mechanism with a high reduction ratio, then, in order to satisfy the load torque when the valve is nearly fully closed, the operating speed will have to be slow across the entire scope of valve opening, and thus the time required for operation will be too long and the controllability will be poor. On the other hand, when a high-power motor (combined with a gear mechanism with a low reduction ratio) is used, then although the time for the operation will be short, there will be surplus torque when the valve is near the fully open position, which would increase the cost of the motor.
Note that there are a large number of technologies for switching the power depending on the torque, and the like (referencing, for example, Japanese Unexamined Patent Application Publication 2008-151293), where mechanisms are provided for switching the power transmission depending on the torque, but this leads to concerns about the complexity of the mechanisms and about increases in size. Moreover, while there are also technologies for controlling the power of the motor depending on the load torque on the motor (referencing, for example, Japanese Unexamined Patent Application Publication 2009-33913), these require complex control circuits that are dedicated to torque control, for example, load torque detecting circuits, which increases costs. Moreover, in the flow rate controlling valve disclosed in Japanese Unexamined Patent Application Publication H8-247323, even though the opening information is used to increase the torque to the large torque that is required when the valve is in the nearly fully closed position, this produces the possibility of supplying excess torque in other areas of the opening, such as when partially opened. Producing excess torque results in wasted electrical power.
The present invention was created in order to solve these issues, and the object thereof is to provide a flow rate controlling valve able to supply the appropriate torque across the entirety of the opening range, doing so at a low cost, without a complex structure.